Question: Simplify the following expression: $x = \dfrac{4}{9n} - \dfrac{1}{10n}$
In order to subtract expressions, they must have a common denominator. The smallest common denominator is the least common multiple of $9n$ and $10n$ $\lcm(9n, 10n) = 90n$ $ x = \dfrac{10}{10} \cdot \dfrac{4}{9n} - \dfrac{9}{9} \cdot \dfrac{1}{10n} $ $x = \dfrac{40}{90n} - \dfrac{9}{90n}$ $x = \dfrac{40 -9}{90n}$ $x = \dfrac{31}{90n}$